465 research outputs found
Multiple Projection Optical Diffusion Tomography with Plane Wave Illumination
We describe a new data collection scheme for optical diffusion tomography in
which plane wave illumination is combined with multiple projections in the slab
imaging geometry. Multiple projection measurements are performed by rotating
the slab around the sample. The advantage of the proposed method is that the
measured data can be much more easily fitted into the dynamic range of most
commonly used detectors. At the same time, multiple projections improve image
quality by mutually interchanging the depth and transverse directions, and the
scanned (detection) and integrated (illumination) surfaces. Inversion methods
are derived for image reconstructions with extremely large data sets. Numerical
simulations are performed for fixed and rotated slabs
Bubble-Driven Inertial Micropump
The fundamental action of the bubble-driven inertial micropump is
investigated. The pump has no moving parts and consists of a thermal resistor
placed asymmetrically within a straight channel connecting two reservoirs.
Using numerical simulations, the net flow is studied as a function of channel
geometry, resistor location, vapor bubble strength, fluid viscosity, and
surface tension. Two major regimes of behavior are identified: axial and
non-axial. In the axial regime, the drive bubble either remains inside the
channel or continues to grow axially when it reaches the reservoir. In the
non-axial regime the bubble grows out of the channel and in all three
dimensions while inside the reservoir. The net flow in the axial regime is
parabolic with respect to the hydraulic diameter of the channel cross-section
but in the non-axial regime it is not. From numerical modeling, it is
determined that the net flow is maximal when the axial regime crosses over to
the non-axial regime. To elucidate the basic physical principles of the pump, a
phenomenological one-dimensional model is developed and solved. A linear array
of micropumps has been built using silicon-SU8 fabrication technology, and
semi-continuous pumping across a 2 mm-wide channel has been demonstrated
experimentally. Measured variation of the net flow with fluid viscosity is in
excellent agreement with simulation results.Comment: 18 pages, 18 figures, single colum
Bound whispering gallery modes in circular arrays of dielectric spherical particles
Low-dimensional ordered arrays of optical elements can possess bound modes
having an extremely high quality factor. Typically, these arrays consist of
metal elements which have significantly high light absorption thus restricting
performance. In this paper we address the following question: can bound modes
be formed in dielectric systems where the absorption of light is negligible?
Our investigation of circular arrays of spherical particles shows that (1) high
quality modes in an array of 10 or more particles can be attained at least for
a refractive index , so optical materials like TiO or GaAs can
be used; (2) the most bound modes have nearly transverse polarization
perpendicular to the circular plane; (3) in a particularly interesting case of
TiO particles (rutile phase, ), the quality factor of the most
bound mode increases almost by an order of magnitude with the addition of 10
extra particles, while for particles made of GaAs the quality factor increases
by almost two orders of magnitude with the addition of ten extra particles. We
hope that this preliminary study will stimulate experimental investigations of
bound modes in low-dimensional arrays of dielectric particles.Comment: Submitted to Physical Review
Homogenization of Maxwell's equations in periodic composites
We consider the problem of homogenizing the Maxwell equations for periodic
composites. The analysis is based on Bloch-Floquet theory. We calculate
explicitly the reflection coefficient for a half-space, and derive and
implement a computationally-efficient continued-fraction expansion for the
effective permittivity. Our results are illustrated by numerical computations
for the case of two-dimensional systems. The homogenization theory of this
paper is designed to predict various physically-measurable quantities rather
than to simply approximate certain coefficients in a PDE.Comment: Significantly expanded compared to v1. Accepted to Phys.Rev.E. Some
color figures in this preprint may be easier to read because here we utilize
solid color lines, which are indistinguishable in black-and-white printin
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Plug-In Hybrid Electric Vehicle Value Proposition Study: Phase 1, Task 2: Select Value Propositions/Business Model for Further Study
The Plug-In Hybrid Electric Vehicle (PHEV) Value Propositions Workshop held in Washington, D.C. in December 2007 served as the Task 1 Milestone for this study. Feedback from all five Workshop breakout sessions has been documented in a Workshop Summary Report, which can be found at www.sentech.org/phev. In this report, the project team compiled and presented a comprehensive list of potential value propositions that would later serve as a 'grab bag' of business model components in Task 2. After convening with the Guidance and Evaluation Committee and other PHEV stakeholders during the Workshop, several improvements to the technical approach were identified and incorporated into the project plan to present a more realistic and accurate case study and evaluation. The assumptions and modifications that will have the greatest impact on the case study selection process in Task 2 are described in more detail in this deliverable. The objective of Task 2 is to identify the combination of value propositions that is believed to be achievable by 2030 and collectively hold promise for a sustainable PHEV market by 2030. This deliverable outlines what the project team (with input from the Committee) has defined as its primary scenario to be tested in depth for the remainder of Phase 1. Plans for the second and third highest priority/probability business scenarios are also described in this deliverable as proposed follow up case studies in Phase 2. As part of each case study description, the proposed utility system (or subsystem), PHEV market segment, and facilities/buildings are defined
Fluctuations and scaling of inverse participation ratios in random binary resonant composites
We study the statistics of local field distribution solved by the
Green's-function formalism (GFF) [Y. Gu et al., Phys. Rev. B {\bf 59} 12847
(1999)] in the disordered binary resonant composites. For a percolating
network, the inverse participation ratios (IPR) with are illustrated, as
well as the typical local field distributions of localized and extended states.
Numerical calculations indicate that for a definite fraction the
distribution function of IPR has a scale invariant form. It is also shown
the scaling behavior of the ensemble averaged described by the
fractal dimension . To relate the eigenvectors correlations to resonance
level statistics, the axial symmetry between and the spectral
compressibility is obtained.Comment: 7 pages, 6 figures, accepted by Physical Review
Angiogenesis: A Cellular Response to Traumatic Injury
The development of new vasculature plays a significant role in a number of chronic disease states, including neoplasm growth, peripheral arterial disease, and coronary artery disease, among many others. Traumatic injury and hemorrhage, however, is an immediate, often dramatic pathophysiologic insult which can also necessitate neovascularization to promote healing. Traditional understanding of angiogenesis involved resident endothelial cells branching outward from localized niches in the periphery. Additionally, there are a small number of circulating endothelial progenitor cells which participate directly in the process of neovessel formation. The bone marrow stores a relatively small number of so-called pro-angiogenic hematopoietic progenitor cells (PACs) â that is, progenitor cells of a hematopoietic potential that differentiate into key structural cells and stimulate or otherwise support local cell growth/differentiation at the site of angiogenesis. Following injury, a number of cytokines and intercellular processes are activated or modulated to promote development of new vasculature. These processes initiate and maintain a robust response to vascular insult, allowing new vessels to canalize and anastomose and provide timely oxygen delivering to healing tissue. Ultimately as we better understand the key players in the process of angiogenesis we can look to develop novel techniques to promote healing following injury
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Plug-In Hybrid Electric Vehicle Value Proposition Study: Interim Report: Phase I Scenario Evaluation
Plug-in hybrid electric vehicles (PHEVs) offer significant improvements in fuel economy, convenient low-cost recharging capabilities, potential environmental benefits, and decreased reliance on imported petroleum. However, the cost associated with new components (e.g., advanced batteries) to be introduced in these vehicles will likely result in a price premium to the consumer. This study aims to overcome this market barrier by identifying and evaluating value propositions that will increase the qualitative value and/or decrease the overall cost of ownership relative to the competing conventional vehicles and hybrid electric vehicles (HEVs) of 2030 During this initial phase of this study, business scenarios were developed based on economic advantages that either increase the consumer value or reduce the consumer cost of PHEVs to assure a sustainable market that can thrive without the aid of state and Federal incentives or subsidies. Once the characteristics of a thriving PHEV market have been defined for this timeframe, market introduction steps, such as supportive policies, regulations and temporary incentives, needed to reach this level of sustainability will be determined. PHEVs have gained interest over the past decade for several reasons, including their high fuel economy, convenient low-cost recharging capabilities, potential environmental benefits and reduced use of imported petroleum, potentially contributing to President Bush's goal of a 20% reduction in gasoline use in ten years, or 'Twenty in Ten'. PHEVs and energy storage from advanced batteries have also been suggested as enabling technologies to improve the reliability and efficiency of the electric power grid. However, PHEVs will likely cost significantly more to purchase than conventional or other hybrid electric vehicles (HEVs), in large part because of the cost of batteries. Despite the potential long-term savings to consumers and value to stakeholders, the initial cost of PHEVs presents a major market barrier to their widespread commercialization. The purpose of this project is to identify and evaluate value-added propositions for PHEVs that will help overcome this market barrier. Candidate value propositions for the initial case study were chosen to enhance consumer acceptance of PHEVs and/or compatibility with the grid. Potential benefits of such grid-connected vehicles include the ability to supply peak load or emergency power requirements of the grid, enabling utilities to size their generation capacity and contingency resources at levels below peak. Different models for vehicle/battery ownership, leasing, financing and operation, as well as the grid, communications, and vehicle infrastructure needed to support the proposed value-added functions were explored during Phase 1. Rigorous power system, vehicle, financial and emissions modeling were utilized to help identify the most promising value propositions and market niches to focus PHEV deployment initiatives
Identification of population characteristics through implementation of the Comprehensive Diabetic Retinopathy Program
Abstract
Background
Diabetic retinopathy is the most common cause of blindness in working-age adults. Characteristics of patients with diabetes presenting to a retina subspecialty clinic have not been adequately studied, limiting our ability to risk stratify patients with diabetic retinopathy. Our goal is to describe an innovative program that collects structured, longitudinal data on patients with diabetes in a retina clinic, and identifies population characteristics to define patient risk stratification.
Methods
Demographics, body-mass index, blood pressure, hemoglobin A1c, smoking history, diabetes type, diabetes duration, kidney disease history, and diagnosis codes were collected on all patients with diabetes at the Kellogg Eye Center retina clinic. A mixed effects negative binomial regression was then performed to assess visit frequency as a function of these variables. Visit frequency was used as a marker for cost of care. A subgroup of patients was surveyed about knowledge of diabetes management goals and barriers to better self-management.
Results
There were 2916 patients in the cohort with 1014 in the subgroup. The cohort was predominantly Caucasian (74.5%), with a mean age of 64âyears (range 13â99) and a relatively even distribution of sex (53.2% men). The mean maximum hemoglobin A1c was 8.0% (range 4.3â15.7%), and 57.1% had a diagnosis of diabetic retinopathy. Patients averaged 3.9 visits (range 1â27) during the 18-month study period. Blood pressure and duration of diabetes were positively associated with visit frequency (pâ<â0.0001, pâ<â0.0001, respectively). Of the surveyed patients, 87.6% knew their goal hemoglobin A1c, while only 45.9% identified the correct blood pressure goal. The most common reported barrier to better self-management was âitâs just not workingâ (47.1%).
Conclusions
Implementation of this program enables the creation of a longitudinal dataset on patients with diabetes. Resulting data can be used to improve quality of care provided to patients at a retina clinic. The findings suggest considerable healthcare resources are being directed to a small patient population. This enhanced understanding of characteristics of patients with diabetes will improve efforts to preserve vision and utilize health system resources efficiently.https://deepblue.lib.umich.edu/bitstream/2027.42/149131/1/40842_2019_Article_79.pd
Unraveling biogeochemical phosphorus dynamics in hyperarid Marsâanalogue soils using stable oxygen isotopes in phosphate
With annual precipitation less than 20 mm and extreme UV intensity, the Atacama Desert in northern Chile has long been utilized as an analogue for recent Mars. In these hyperarid environments, water and biomass are extremely limited, and thus, it becomes difficult to generate a full picture of biogeochemical phosphateâwater dynamics. To address this problem, we sampled soils from five Atacama study sites and conducted three main analysesâstable oxygen isotopes in phosphate, enzyme pathway predictions, and cell culture experiments. We found that high sedimentation rates decrease the relative size of the organic phosphorus pool, which appears to hinder extremophiles. Phosphoenzyme and pathway prediction analyses imply that inorganic pyrophosphatase is the most likely catalytic agent to cycle P in these environments, and this process will rapidly overtake other P utilization strategies. In these soils, the biogenic δ18O signatures of the soil phosphate (δ18OPO4) can slowly overprint lithogenic δ18OPO4 values over a timescale of tens to hundreds of millions of years when annual precipitation is more than 10 mm. The δ18OPO4 of calciumâbound phosphate minerals seems to preserve the δ18O signature of the water used for biogeochemical P cycling, pointing toward sporadic rainfall and gypsum hydration water as key moisture sources. Where precipitation is less than 2 mm, biological cycling is restricted and bedrock δ18OPO4 values are preserved. This study demonstrates the utility of δ18OPO4 values as indicative of biogeochemical cycling and hydrodynamics in an extremely dry Marsâanalogue environment
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